Whisker-reinforced ceramic containing aluminum oxynitride and method of making the same

ABSTRACT

A process of making aluminum oxynitride powder including the steps of: forming a powder mixture by mixing alumina powder and aluminum nitride powder according to the following formula: ((4−x)/3) alumina and x aluminum nitride wherein x is in mole percent and ranges between about 0.31 and about 0.61; adding between about 0.1 mole percent and about 1.0 mole percent of pure aluminum powder to the powder mixture; and reacting the powder mixture containing aluminum at a temperature between about 1600° C. and about 1900° C. for a duration between about 2 hours and about 24 hours in a flowing nitrogen atmosphere so as to form aluminum oxynitride.

RELATED APPLICATIONS

This application is a divisional patent application of co-pending U.S.patent application Ser. No. 11/234,013 filed on Sep. 23, 2005, pendingwhich is divisional patent application of co-pending U.S. patentapplication Ser. No. 11/101,260 filed on Apr. 7, 2005 now U.S. Pat. No.7,262,145, pending which is a continuation-in-part of U.S. patentapplication Ser. No. 10/831,383, filed on Apr. 23, 2004, abandoned.

BACKGROUND OF THE INVENTION

The present invention pertains to a whisker-reinforced ceramic and amethod for making the same. More specifically, the invention pertains toa whisker-reinforced ceramic that contains aluminum oxynitride, andoptionally, other materials, and a method for making the same.

Whisker-reinforced materials such as, for example, whisker-reinforcedceramics have been known for some time. In this regard, U.S. Pat. No.4,543,345 to Wei describes a silicon carbide whisker-reinforced aluminaceramic material. U.S. Pat. No. 4,789,277 to Rhodes et al. and U.S. Pat.No. 4,961,757 to Rhodes et al. each disclose a ceramic cutting toolwherein the ceramic is a silicon carbide-whisker-reinforced alumina.

U.S. Pat. No. 6,447,896 to Augustine discloses a coated ceramic cuttingtool wherein the ceramic contains silicon carbide whiskers. According tothe Augustine patent, there is a listing of many ceramics suitable foruse as a whisker-reinforced ceramic. These ceramics include, among many,alumina, titanium carbonitride, zirconium oxide and aluminum oxinitride.

Further, European Patent No. 0 247 630 B1 to NGK Spark Plug pertains toa ceramic material that is useful as a cutting tool. The ceramicsubstrate is based on a matrix composed of at least one materialselected from the group consisting of Al₂O₃, AlN, AlON, 3Al₂O₃.2SiO₂(mullite) and TiC, and the substrate further comprises 5 to 50% byweight of SiC whiskers with respect to said substrate.

European Patent No. 0 861 219 B1 to Kennametal Inc. (as well as U.S.Pat. No. 5,955,390 and U.S. Pat. No. 6,204,213 B1 to Mehrotra et al.that are assigned to Kennametal Inc.) discloses titaniumcarbonitride-alumina-silicon carbide whisker ceramics. In theseceramics, the titanium carbonitride is the dominant matrix component.

While the above ceramic materials exhibit satisfactory properties, atleast in certain situations, there still remains the need to develop newand useful ceramic materials. This is especially true for ceramicmaterials that are useful as cutting tools.

Heretofore, in experimental work done in the in-house facilities ofKennametal Inc. of Latrobe, Pa. 15650 USA (the assignee of the presentpatent application), the inventors have considered the use of aluminumoxynitride as a component of a ceramic material useful as a cuttingtool. Aluminum oxynitride has mechanical properties that are similar tothose of alumina, but it has a higher strength and a lower coefficientof thermal expansion than alumina. In light of these properties, theinclusion of aluminum oxynitride in a ceramic was thought to improve itsthermal shock resistance. It was believed that the principal failuremechanism of alumina-silicon carbide whisker reinforced ceramic cuttingtools in turning nickel-based high temperature alloys was depth-of-cutnotch. There was the belief that this failure mechanism, i.e.,depth-of-cut notch, was related to the thermal shock resistance and theimpact strength of the cutting tool material.

Still in experimental work the inventors did in the past in the in-housefacilities of Kennametal Inc., the typical way to make a ceramicmaterial that contained aluminum oxynitride and silicon carbide whiskerswas to use alumina and aluminum nitride as a part of the startingcomponents. These starting components were hot-pressed at temperatureson the order of about 1950 degrees Centigrade. It was found that by hotpressing this powder mixture containing aluminum nitride and siliconcarbide whiskers at temperatures on the order of about 1950 degreesCentigrade, the aluminum nitride and the silicon carbide whiskers formeda solid solution that caused a strong interface there between. Thisinterface prevented whisker pull-out, i.e., pull-out of the siliconcarbide whiskers from the ceramic matrix. The absence of whiskerpull-out resulted in the degradation of the performance properties ofthe ceramic cutting tool.

In regard to whisker pull-out, U.S. Reissue Pat. No. 34,446 to Wei setsforth a discussion of whisker pull-out at Column 2, lines 30 through 53:

-   -   The use of the single crystal whiskers in the ceramic composite        provide a significant improvement in the fracture toughness of        the composite due to their ability to absorb cracking energy.        More specifically, in a ceramic matrix where the SiC        whisker-matrix interface sheer strength is relatively low as        provided by radial tensile stresses across the whisker-matrix        bond a process termed “whisker pull-out” occurs during cracking        to absorb the cracking energy and effectively reduce the        tendency to crack and also inhibit crack propagation. Whisker        pull-out occurs as the matrix is subjected to crack-forming        stresses. As the crack-front propagates into the composite many        of the whiskers which span the crack line and extend into the        ceramic matrix on opposite sides of the crack must be either        fractured or pulled out of the matrix in order for the crack to        grow or propagate through the ceramic. Since the single crystal        SiC whiskers possess sufficient tensile strength so as to resist        fracturing they must be pulled out of the matrix for the crack        to propagate. As these whiskers are pulled out of the matrix        they exhibit considerably bridging forces on the face of the        crack and effectively reduce the stress intensity at the crack        tip so as to absorb the cracking energy.

In experimental work done by the inventors in the in-house facilities ofKennametal Inc., when titanium carbonitride was a component in thestarting powder, along with aluminum nitride and alumina and siliconcarbide whiskers, it was found that the titanium carbonitride and thesilicon carbide considerably delayed the formation of the aluminumoxynitride. In order to overcome this consequence, the hot-pressingtemperature had to be raised to such a level that the silicon carbidewhiskers suffered damage.

In experimental work done by the inventors in the in-house facilities ofKennametal Inc., it was also found that when using aluminum nitride andalumina to form the aluminum oxynitride, it was difficult to control thefinal composition of the ceramic. More specifically, this was due to thedifficulty associated with controlling the amount of aluminum oxynitrideproduced when using aluminum nitride and alumina in the startingpowders.

Thus, it can be seen that it would be highly desirable to provide animproved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride.

It can also be seen that it would be highly desirable to provide animproved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride wherein the whiskers exhibit satisfactorypull-out which can be considered to be satisfactory crack-bridgingpull-out from the ceramic matrix.

Further, it can be seen that it would be highly desirable to provide animproved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride wherein the hot-pressing of the powdermixture occurs at a temperature low enough so as to not damage thesilicon carbide whiskers and minimize the grain growth of the aluminumoxynitride.

Finally, it can be seen that it would be highly desirable to provide animproved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride wherein there is control over the amount ofaluminum oxynitride in the ceramic.

SUMMARY OF THE INVENTION

In summary, the present invention is directed to a ceramic body (and itsmethod of manufacture), such as a metalcutting tool, having about 2 toabout 40 volume percent ceramic whiskers distributed in a matrixcomprising aluminum oxynitride and, optionally, one or more ceramicadditives. The aluminum oxynitride forms at least 10 volume percent, andup to about 98 volume percent, of the ceramic. Preferably, the ceramiccontains at least 30 volume percent, more preferably at least 40 volumepercent, and most preferably at least 50 volume percent aluminumoxynitride.

The densified ceramic according to the present invention preferably hasan aluminum oxynitride grain size of less than 4 μm, preferably lessthan 3 μm, more preferably less than or equal to 2 μm, and mostpreferably less than or equal to 1 μm.

The ceramic additive, when present, is preferably titanium carbonitride,and/or alumina, and/or zirconia, and/or one or more sintering aids.

When titanium carbonitride is added, it is added at levels of up to 40volume percent, and preferably 1 to 40 volume percent, and morepreferably 5 to 15 volume percent.

When alumina is added, it is added at levels up to 40 volume percent,preferably 1 to 40 volume percent.

In one form thereof, the invention is a ceramic body that comprises amatrix that includes aluminum oxynitride. The ceramic body furtherincludes whiskers distributed throughout the matrix. The aluminumoxynitride comprises between about 60 volume percent and about 98 volumepercent of the ceramic body. The whiskers comprise between about 2volume percent and about 40 volume percent of the ceramic body.

In another form thereof, the invention is a ceramic body that includes amatrix comprising aluminum oxynitride and a ceramic additive other thanaluminum oxynitride. There are whiskers distributed throughout thematrix. The aluminum oxynitride comprises between about 30 volumepercent and about 70 volume percent of the ceramic body. The ceramicadditive comprises between about 10 volume percent and about 40 volumepercent of the ceramic body. The whiskers comprise between about 2volume percent and about 40 volume percent, and more preferably betweenabout 15 volume percent and 35 volume percent, of the ceramic body.

In yet another form thereof, the invention is a ceramic body thatincludes a matrix that comprises aluminum oxynitride and alumina and aceramic additive other than aluminum oxynitride or alumina. There arewhiskers distributed throughout the matrix. The aluminum oxynitridecomprises between about 10 volume percent and about 25 volume percent ofthe ceramic body. The alumina comprises between about 25 volume percentand about 40 volume percent of the ceramic. The ceramic additivecomprises between about 15 volume percent and about 35 volume percent ofthe ceramic body. The whiskers comprise between about 2 volume percentand about 40 volume percent, and more preferably between about 15 volumepercent and 35 volume percent, of the ceramic body.

In still another form thereof, the invention is a ceramic body thatcomprises a matrix that includes aluminum oxynitride and zirconia. Thereare whiskers distributed throughout the matrix. The aluminum oxynitridecomprises between about 30 volume percent and about 60 volume percent ofthe ceramic body. The zirconia comprises between about 1 volume percentand about 10 volume percent of the ceramic body. The whiskers comprisebetween about 2 volume percent and about 40 volume percent of theceramic body.

In yet another form thereof, the invention is a process to make aceramic body comprising the steps of: providing a starting powdermixture comprising aluminum oxynitride powder that contains less than orequal to about 0.1 weight percent aluminum nitride, ceramic whiskers,and a ceramic additive other than aluminum oxynitride; and consolidatingthe starting powder mixture into the ceramic body.

In another form thereof the invention is a process to make a ceramicbody comprising the steps of: providing a starting powder mixturecomprising between about 40 and about 98 volume percent aluminumoxynitride and between about 2 and about 40 volume percent whiskers; andconsolidating the starting powder into the ceramic body.

In yet another form thereof, the invention is a process to make aceramic body comprising the steps of: providing a starting powdermixture comprising between about 40 and about 98 volume percent aluminumoxynitride and between about 2 and about 40 volume percent whiskers; andhot-pressing the starting powder into the ceramic body at a temperatureless than or equal to about 1750° C.

In still another form, the invention is a process of making aluminumoxynitride powder comprising the steps of: forming a powder mixture bymixing alumina powder and aluminum nitride powder according to thefollowing formula: ((4−x)/3) alumina and x aluminum nitride wherein x isin mole percent and ranges between about 0.31 and about 0.61; addingbetween about 0.1 mole percent and about 1.0 mole percent of purealuminum powder to the powder mixture; and reacting the powder mixturecontaining aluminum at a temperature between about 1600° C. and about1900° C. for a duration between about 2 hours and about 24 hours in aflowing nitrogen atmosphere so as to form aluminum oxynitride.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings that form a part ofthis patent application:

FIG. 1 is an isometric view of an RNG43T0320 style of ceramic cuttingtool wherein the ceramic of the invention is useful as a cutting tool ofthis style;

FIG. 2 is a photomicrograph taken by scanning electron microscopy (SEM)at a magnification equal to 3000× of the microstructure of Example No.1; and

FIG. 3 is a photomicrograph taken by scanning electron microscopy (SEM)at a magnification equal to 3000× of the microstructure of Example No.4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 shows a RNG43T0320 style of cuttingtool generally designated as 20. Cutting tool 20 has a rake face 22 anda flank face 24. The rake face 22 and the flank face 24 intersect toform a cutting edge 26 at the juncture thereof wherein the cutting edgeis of a generally circular shape. While the cutting tool 20 is shown asa generally cylindrical shaped cutting tool, it should be appreciatedthat the composition of the present invention can be made into othergeometries of cutting tools. Further, although the specific embodimentshown is a cutting tool, it should be appreciated that the ceramiccomposition of the invention may be used for other products, such as,for example, wear products and impact resistant parts, as well as otherstructural applications.

Cutting tool 20 is not coated. The substrate of ceramic cutting tool 20contains aluminum oxynitride and titanium carbonitride and siliconcarbide whiskers.

As an alternative composition to the above ceramic composition, theceramic substrate may further include alumina so that the ceramicsubstrate comprises aluminum oxynitride and titanium carbonitride andalumina and silicon carbide whiskers. The ceramic substrate containsalumina so as to provide improved chemical wear resistance.

For each one of the above compositions, applicants contemplate that thetitanium carbonitride may be replaced in whole or in part by one or moreof the following materials separately or in solid solution with eachother or one or more other elements: hafnium carbonitride and zirconiumcarbonitride, boron carbide, titanium diboride, zirconium diboride, andhafnium diboride. Also for each one of the above compositions, thesilicon carbide whiskers can be replaced in whole or in part by one ormore other ceramic whiskers such as, for example, titanium carbidewhiskers and/or titanium carbonitride whiskers and/or titanium nitridewhiskers either alone or in any combination thereof.

In order to make the ceramic cutting tool 20, there is a starting powdermixture that comprises aluminum oxynitride, titanium carbonitride, andsilicon carbide whiskers along with a sintering aid. One exemplarysintering aid is yttria. Other sintering aids include magnesia,zirconia, yttrium aluminum garnet, ytterbia and other rare earth oxides(e.g., lanthanum oxide, europium oxide, erbium oxide, cerium oxide,praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide,gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, andthulium oxide). In the one alternative ceramic composition, the startingpowder mixture comprises aluminum oxynitride, titanium carbonitride,alumina, and silicon carbide whiskers along with a sintering aid suchas, for example, yttria. In the other alternative ceramic composition,the starting powder mixture for the ceramic comprises aluminumoxynitride, alumina, silicon carbide and a sintering aid (e.g., yttria,magnesia, or the like). The sintering aid(s) can be present in an amountof less than or equal to about 3 volume percent of the starting powdermixture. More preferably, the sintering aid(s) can be present in anamount of less than or equal to about 1 volume percent of the startingpowder mixture. In the case of zirconia, the zirconia can be present athigher levels, for example, in an amount on the order of about 5 volumepercent as shown in Example No. 3 set forth hereinafter to furtherimprove fracture toughness.

For all of the starting powder mixtures, the aluminum oxynitridestarting powder is a high purity powder so that it does not contain adetectable content of residual aluminum nitride and preferably does notcontain a detectable content of residual alumina. In this regard, theabsence of a detectable content of residual aluminum nitride or adetectable content of residual alumina when using standard Bragg x-raydiffraction technique means that the residual aluminum nitride ispresent in an amount less than or equal to about 0.1 weight percent andthat the residual alumina is present in an amount less than or equal toabout 0.1 weight percent. It is most preferable that the aluminumoxynitride starting powder does not contain any residual aluminumnitride or any residual alumina.

Applicants believe that there are some advantages associated with usingaluminum oxynitride starting powder that does not contain a detectablecontent of residual aluminum nitride or a detectable content of residualalumina. In this regard, one advantage of the high purity aluminumoxynitride starting powder is that there is a known content of aluminumoxynitride that results in better predictability as to the hot pressingconditions that are necessary to fully react the components during theformation of the ceramic. This predictability permits the use of shortertimes and lower temperatures to hot press or consolidate the powdermixture into the ceramic. The use of shorter times and lowertemperatures to hot press the ceramic result in less reaction betweenthe matrix components and the whiskers (e.g., silicon carbide whiskers)so that the whiskers maintain their ability to adequately pull-out ofthe matrix, i.e., to reinforce the matrix as measured by the fracturetoughness of the material.

The above advantages are in contrast to a ceramic formed using a powdermixture that contains alumina and aluminum nitride. In this regard,there is less control over the reaction to form the ceramic wherein theprocess uses a powder mixture that contains alumina and aluminumnitride. Thus, the hot pressing parameters to form the ceramic mustinclude a time that is longer and a temperature that is higher so as tobe able to fully react the alumina and the aluminum nitride. The use oflonger times and higher temperatures results in a reduction in theefficiency of the hot pressing process because it takes more time andenergy to form the ceramic. In addition, the use of longer times andhigher temperatures results in more reaction between the whiskers (e.g.,silicon carbide whiskers) and the matrix components and this can lead toa reduction in the ability of the whiskers to adequately pull-out of thematrix.

By reducing or eliminating the presence of residual aluminum nitride inthe aluminum oxynitride starting powder, the present invention providesthe advantage of reducing or eliminating a reaction between the siliconcarbide whiskers and the residual aluminum nitride wherein the siliconcarbide and the aluminum nitride form a solid solution that can degradethe performance of the material. In addition, by reducing or eliminatingthe presence of residual alumina in the aluminum oxynitride startingpowder, the present invention provides the advantage of reducing oreliminating the potential for the residual alumina to form a liquidphase with the aluminum oxynitride at high temperatures wherein theformed liquid phase can degrade the performance of the material.

Still referring to the advantages, applicants believe that by using thehigh purity aluminum oxynitride starting powder, the hot pressingtemperature can be about 1800° C. or less, and preferably 1750° C. orless. For example, one range for the hot-pressing temperature is betweenabout 1600° C. and about 1800° C. This is in contrast to a process thatuses a starting powder that contains alumina and aluminum nitridewherein such process requires a hot pressing temperature in the range ofabout 1900° C. to about 1975° C. to achieve essentially fulldensification.

The aluminum oxynitride starting powder is also fine wherein the averageparticle size is no more than about 5 micrometers, preferably, no morethan about 1.0 micrometers. The high purity aluminum oxynitride powderis made by reaction sintering alumina and aluminum nitride in a nitrogenatmosphere. The time and temperature and the pressure of the sinteringprocess are carefully controlled so that the resulting aluminumoxynitride does not contain any detectable alumina or any detectablealuminum nitride.

In regard to the process parameters necessary to make the aluminumoxynitride starting powder, its is believed that the following reactiontakes place:((4−x)/3) alumina+x aluminum nitride→Al_((8+x)/3) O_(4−x) N_(x)wherein x is in mole percent and x ranges between about 0.31 and about0.61. The above reaction takes place within the following processparameters: a temperature range between about 1600 degrees Centigradeand about 1900 degrees Centigrade for a duration of between about 2hours and about 24 hours in a flowing nitrogen atmosphere. For thealuminum oxynitride used in the examples that are set forth below xequals 0.35 and an effective amount of pure aluminum powder was addedfor balancing the effects of the nitrogen atmosphere, and preferablythis amount ranges between about 0.1 to about 0.2 mole percent of purealuminum powder. However, it should be appreciated that the amount ofpure aluminum powder could range between about 0.2 mole percent andabout 1.0 mole percent of the starting powder mixture. The aluminumoxynitride is a cubic spinel crystalline phase (gamma phase) that hasthe preferred formula: Al_(2.78)O_(3.65)N_(0.35).

Example No. 1 is a ceramic of the present invention. Example No. 1 wasmade using the following starting powder mixture: about 26.2 volumepercent titanium carbonitride powder wherein the titanium carbonitridepowder had the following properties: molar ratio of carbon to nitrogenis 50:50 and the average particle size is about 3 micrometers and theoxygen content is less than about 1 weight percent; about 48.6 volumepercent aluminum oxynitride wherein the aluminum oxynitride powder hadthe following properties: no detectable aluminum nitride or alumina andthe average particle size was less than about 3 micrometers; about 25.0volume percent silicon carbide whiskers wherein the silicon carbidewhiskers were the SC-9 grade of silicon carbide whiskers obtained fromAdvanced Composite Materials Corporation of Greer, S.C., and the siliconcarbide whiskers had the following properties: average diameter equal toabout 0.6 micrometers, and a length of about 10-80 micrometers with anaverage aspect ratio equal to about 75, and the whisker content greaterthan about 90 percent; and about 0.2 volume percent yttria wherein theyttria powder had the following properties: average particle size equalto about 0.7 micrometers and a purity equal to greater than about 99.95percent.

The starting powder mixture for Example No. 1 was formed by blending thealuminum oxynitride and the titanium carbonitride and the yttriapowders, and then the silicon carbide whiskers were blended into thepowder mixture so that they were thoroughly and uniformly distributedthroughout the starting powder mixture. The powder mixture was thenhot-pressed under the following conditions: a temperature of about 1700degrees Centigrade for a duration of about one hour under a pressure ofabout 5000 pounds per square inch (psi) (34.5 MPa) and in either vacuumor in a protective atmosphere (e.g., nitrogen).

Table 1 set forth below reports selected physical properties of theExample No. 1 ceramic material. Referring to the properties, the densityis reported in grams per cubic centimeter. The density was measuredaccording to the procedure set forth in ASTM B311-93 (2000) (Test Methodfor Density Determination for Powder Metallurgy (Materials ContainingLess Than Two Percent Porosity)). The Young's Modulus (E) is reported ingigapascals (GPa) and was determined per ASTM E111-97 Standard TestMethod for Young's Modulus, Tangent Modulus, and Chord Modulus. TheVicker's Hardness Number (VHN) is reported in gigapascals (GPa) and wasdetermined per ASTM E384-99e1, Standard Test Method for Microindentationof Materials (at a load equal to 18.5 kilograms). The fracture toughness(K_(IC)) is reported in M·Pa·m^(1/2) and was determined per the methodset forth in the article by Evans and Charles entitled “FractureToughness Determinations by Indentation”, Journal American CeramicSociety 59, Nos. 7-8. pages 371-372 (1976) [at a load equal to 18.5kilograms].

TABLE I Selected Properties of Example No. 1 Fracture Young's VHNToughness (K_(IC)) Property Density (g/cc) Modulus (GPa) (GPa) Evans &Charles Example 3.94 [theoretical 394 19.13 5.80 No. 1 density equal to3.96 g/cc]

FIG. 2 is a SEM photomicrograph of the microstructure of the ceramic ofExample No. 1. FIG. 2 shows the homogeneously distributed needle-shapedsilicon carbide whiskers and the irregular shaped titanium carbonitridewherein each one of these can be easily distinguished from the aluminumoxynitride. In this regard, the titanium carbonitride is the light phaseand the aluminum oxynitride is the darker phase.

As previously mentioned, there are other compositions of the inventiveceramic wherein one of these compositions comprises aluminum oxynitride,titanium carbonitride, alumina and silicon carbide whiskers. For ExampleNo. 2, Table 2 below sets forth the starting powder mixture (there isabout 0.3 volume percent yttria sintering aid not listed in Table 2) involume percent as well as a number of other properties describedhereinafter.

TABLE 2 Starting Powder Composition (in Volume Percent) and SelectedProperties of Example No. 2 Silicon Titanium Aluminum carbide DensityTemperature E VHN K_(IC) E & C Example carbonitride alumina oxynitridewhiskers (g/cc) (° C.) (GPa) (GPa) (MPa · m^(1/2)) 2 22.4% 36.6% 15.7%25.0% 4.02 1700 443 21.45 5.33

The properties of the starting powders in the powder mixture for ExampleNo. 2 are the same as those of the starting powders in Example No. 1 tothe extent that the starting powders are the same. Further, the aluminapowder has the following properties: an average particle size equal toless than about 0.6 micrometers, and an impurity content equal to lessthan about 0.1 weight percent. The processing parameters for Example No.2 are the same as those for Example No. 1. The testing standards used totest Example No. 2 were the same as those used to test Example No. 1.

Example No. 3 is another composition of the inventive ceramic andcomprises titanium carbonitride, aluminum oxynitride, zirconia (possiblysome hafnia) and silicon carbide whiskers. Table 3 below sets forth thestarting powder composition and selected properties of the ceramicmaterial. The properties of the starting powders in the powder mixtureof Example No. 3 are the same as those in Example No. 1 and Example No.2 to the extent that the starting powders are the same. In addition, thezirconia powder component has the following properties: monocliniczirconia that can include some hafnia wherein the average particle sizeis equal to less than about 1.0 micrometers and the sum of the zirconiacontent and the hafnia content is equal to or greater than about 98.5weight percent of the component with the hafnia content equal to lessthan or equal to about 2.5 weight percent of the component. Theprocessing parameters are the same as those of Example No. 1, exceptthat the hot pressing temperature was 1680° C. The testing standardsused to test Example No. 3 were the same as those used to test ExampleNo. 1.

TABLE 3 Starting Powder Composition (in Volume Percent) and SelectedProperties of Example No. 3 Silicon Titanium Aluminum carbide DensityTemperature E VHN K_(IC) E & C Example carbonitride oxynitridewhiskers_(w) Zirconia (g/cc) (° C.) (GPa) (GPa) (MPa · m^(1/2)) 3 22.5%47.5% 25.0% 5.0% 3.99 1680 403 11.44 9.83

One alternative composition of the inventive ceramic comprises aluminumoxynitride, alumina and silicon carbide whiskers. The processingparameters would be expected to be the same as those for Example No. 1.

Example No. 4 is another composition of the inventive ceramic and itcontains aluminum oxynitride, silicon carbide whiskers and a sinteringaid in the form of yttria. Table 4 sets forth the starting powdercomposition and selected properties of the ceramic. The properties ofthe starting powders for Example No. 4 were the same as thosecorresponding starting powders in Examples Nos. 1-3. The processingparameters for Example No. 4 were the same as those for Example No. 1.The test standards used to test Example No. 4 were the same as thoseused to test Example No. 1.

TABLE 4 Starting Powder Composition and Selected Properties of ExampleNo. 4 Silicon Aluminum carbide Density Temperature E VHN K_(IC) E & CExample Yttria oxynitride whiskers_(w) (g/cc) (° C.) (GPa) (GPa) (MPa ·m^(1/2)) 4 0.25 74.75 25.0 3.56 1700 360 17.46 5.80

FIG. 3 is a SEM photomicrograph that shows the microstructure of ExampleNo. 4. In this regard, FIG. 3 shows the SiC whiskers as having aneedle-like shape with a gray color and the balance is the aluminumoxynitride matrix. The bright spots in FIG. 3 are thought to beartifacts of titanium carbonitride from the alumina-titanium carbidemilling media.

Tables 2 and 3 set forth below report metal cutting test results forcutting tools made from selected ones of the ceramic of Example No. 1through Example No. 4 as compared to two other prior art cutting tools.One of the prior art cutting tools, i.e., Tool No. A, has thecomposition equal to about 38 volume percent titanium carbonitride,about 37 volume percent alumina and about 25 volume percent siliconcarbide whiskers. The other prior art cutting tool, i.e.,“Alumina-SiC_(w) Tool” has a typical composition (based upon an analysisthereof) as follows: 69.75 volume percent alumina, between about 25volume percent to about 32.5 volume percent silicon carbide whiskers andabout 0.25 volume percent of sintering aid. The “Alumina-SiC_(w) Tool”is available from at least two commercial sources. One such source isGreenleaf Corporation of Saegertown, Pa. that sells such a ceramiccutting tool under the designation WG-300. Another such source is theSandvik Coromant Company of Sweden that sells such a ceramic cuttingtool under the designation “CC670”.

Table 5 presents test results (mean tool life in minutes) from a wet(flood coolant) turning test of a round bar of INCONEL 718 wherein thecutting parameters were: speed equal to about 900 surface feet perminute (295.3 surface meters per minute), a feed equal to about 0.006inches per revolution (0.152 millimeters per revolution), and a depth ofcut notch equal to 0.06 inches (1.52 millimeters). The cutting tool hadthe following geometry: RNG43T0320. The failure criteria were: flankwear, nose wear, and trail edge wear less than about 0.04 inches (or1.016 millimeters), as well as depth-of-cut notch (DOCN) wear less thanabout 0.08 inches (or 2.032 millimeters).

TABLE 5 Turning Test Results on a Round Bar of INCONEL 718 Tool MeanTool Life (minutes) Example No. 1 6.0 Example No. 2 5.6 Tool A 4.0Alumina-SiC_(w) Tool 6.0

Table 6 presents the test results (mean tool life in minutes) from thewet (flood coolant) turning of a round bar of INCONEL 718 wherein thecutting parameters were: speed equal to about 900 surface feet perminute (295.3 surface meters per minute), a feed equal to about 0.006inches per revolution (0.152 millimeters per revolution), and a depth ofcut equal to 0.06 inches (1.52 millimeters). The cutting tool had thefollowing geometry: RNG43T0320. The failure criteria were: maximum flankwear, nose wear, and trail edge wear less than about 0.04 inches (or1.016 millimeters), as well as depth-of-cut notch (DOCN) wear less thanabout 0.08 inches (or 2.032 millimeters). In Table 3, the designationsalong with the tool life reflect the failure mode wherein “ch” meanschipping, “MW” means maximum wear, and “DN” means depth-of-cut notchwear.

TABLE 6 Turning Test Results (Tool Life in Minutes) on a Round Bar ofINCONEL 718 Mean Tool Life Tool Rep. 1 Rep. 2 Rep. 3 (Minutes) ExampleNo. 1 4.0 ch 6.0 4.2 MW 4.7 Example No. 4 4.0 ch 6.0 ch 5.7 MW 5.2 ToolA 4.0 n/a 6.0 ch 5.0 Alumina-SiC_(w) Tool 4.0 ch 4.5 DN 6.0 ch 4.8

Table 7 presents the test results in tool life in minutes from a turningtest of an eccentric bar of INCONEL 718 wherein the cutting parameterswere: speed equal to about 500 surface feet per minute (164 surfacemeters per minute), a feed equal to about 0.006 inches per revolution(0.152 millimeters per revolution), and a depth of cut equal to0.02-0.04 inches (0.508 to 1.02 millimeters). The cutting tool had thefollowing geometry: RNG43T0320. The failure criteria were: flank wear,nose wear, and trail edge wear less than about 0.04 inches (or 1.016millimeters), as well as depth-of-cut notch (DOCN) wear less than about0.08 inches (or 2.032 millimeters). In Table 3, the designations alongwith the tool life reflect the failure mode wherein “BK” means breakage,and “DN” means depth-of-cut notch wear.

TABLE 7 Turning Test Results on an Eccentric Bar of INCONEL 718 MeanTool Life Tool Rep. 1 Rep. 2 (Minutes) Example No. 4 2.1 DN 4.1 DN 3.1Tool A 3.0 BK 1.6 DN 2.3 Alumina-SiC_(w) Tool 2.0 DN 1.5 DN 1.8

Table 8 presents the test results (in mean tool life in minutes) from aturning test of an eccentric bar of INCONEL 718 wherein the cuttingparameters were: speed equal to about 500 surface feet per minute (164surface meters per minute), a feed equal to about 0.006 inches perrevolution (0.152 millimeters per revolution), and a depth of cut notchequal to 0.02-0.04 inches (0.508 to 1.02 millimeters). The cutting toolhad the following geometry: RNG43T0320. The failure criteria were: flankwear, nose wear, and trailing edge wear less than about 0.04 inches (or1.016 millimeters), as well as depth-of-cut notch (DOCN) wear less thanabout 0.08 inches (or 2.032 millimeters).

TABLE 8 Turning Test Results (Mean Tool Life in Minutes) on a EccentricBar of INCONEL 718 Tool Mean Tool Life (Minutes) Example No. 1 1.8Example No. 2 1.0 Example No. 3 1.4 Tool A 1.7 Alumina-SiC_(w) Tool 2.2

In looking at the test results for the ceramic cutting inserts instraight turning and turning of an eccentric bar, it should beappreciated that these tests show different properties. The straightturning test shows the wear properties of the ceramic cutting insert.The toughness properties of the ceramic cutting insert are shown by theeccentric bar test.

Referring to the results for straight turning of INCONEL 718 reported inTable 5, the performance of the silicon carbide-reinforced aluminumoxynitride-titanium carbonitride ceramic cutting tool was better (6.0vs. 4.0 minutes) than the Tool A ceramic cutting tool and wascompetitive (6.0 vs. 6.0 minutes) with the Alumina-SiC_(w) tool ceramiccutting tool in straight turning of INCONEL 718. Straight turning is ameasure of the wear resistance of the ceramic cutting tool. Theperformance of the aluminum oxynitride-titaniumcarbonitride-alumina-silicon carbide whisker ceramic cutting tool wasbetter than Tool A (5.6 vs. 4.0 minutes), but somewhat less (5.6 vs. 6.0minutes) than, the Alumina-SiC_(w) ceramic cutting tool.

Referring to the results for straight turning of INCONEL 718 as reportedin Table 6, the performance of the silicon carbide-reinforced aluminumoxynitride-titanium carbonitride ceramic cutting tool was slightly less(4.7 vs. 5.0 minutes) than the Tool A ceramic cutting tool andessentially competitive (4.7 vs. 4.8 minutes) with the Alumina-SiC_(w)tool ceramic cutting tool. The performance of the aluminumoxynitride-silicon carbide ceramic cutting tool was slightly better thanTool A (5.2 vs. 5.0 minutes) and also better (5.2 vs. 4.8 minutes) thanthe Alumina-SiC_(w) ceramic cutting tool.

Referring to the test results for turning an eccentric bar of INCONEL718 as reported in Table 7, the performance of the aluminumoxynitride-silicon carbide ceramic cutting tool was better than Tool A(3.1 vs. 2.3 minutes) and also better (3.1 vs. 1.8 minutes) than theAlumina-SiC_(w) ceramic cutting tool. The test of turning an eccentricbar is a measure of the toughness of the ceramic cutting tool.

Referring to the test results for turning an eccentric bar of INCONEL718 as reported in Table 8, the aluminum oxynitride-titaniumcarbonitride-silicon carbide whiskers ceramic cutting tool had slightlybetter (1.8 vs. 1.7 minutes) tool life than Tool A, but less tool life(1.8 vs. 2.2 minutes) than the Alumina-SiC_(w) ceramic cutting tool. Thealuminum oxynitride-titanium carbonitride-alumina-silicon carbidewhiskers ceramic cutting tool had less tool life (1.0 vs. 1.7 minutes)tool life than Tool A, as well as less tool life (1.0 vs. 2.2 minutes)than the Alumina-SiC_(w) ceramic cutting tool. The aluminumoxynitride-titanium carbonitride-zirconia-silicon carbide whiskersceramic cutting tool had less tool life (1.4 vs. 1.7 minutes) tool lifethan Tool A, as well as less tool life (1.4 vs. 2.2 minutes) than theAlumina-SiC_(w) ceramic cutting tool.

Example No. 5 is another embodiment of a ceramic of the presentinvention. Example No. 5 was made using the following starting powdermixture: about 9.07 volume percent titanium carbonitride powder (H. D.Stark grade D) having a molar ratio of carbon to nitrogen of 50:50;about 60.68 volume percent alumina oxynitride powder having thefollowing properties: no detectable aluminum nitride or alumina and anaverage particle size of less than 3 μm; about 30 volume percent ofsilicon carbide whiskers, grade SC-9; and about 0.25 volume percent ofyttria powder, H. C. Stark, grade C.

The powder mixture for Example No. 5 was formed by blending the aluminumoxynitride, titanium carbonitride and yttria powders, and then blendingin the silicon carbide whiskers. The powder mixture was hot pressedunder the following conditions: a temperature of about 1780 degreesCentigrade for a duration of about 1 hour under a pressure of about 35MPa in vacuum. The densified hot pressed billet was then cut and groundinto indexable cutting inserts.

The aluminum oxynitride average grain size of the densified Example No.5 material was about 2 to 3 μm. The excellent hot hardness of thismaterial is shown in Table 9 below:

TABLE 8 Vickers Hot Hardnesses (500 gm), GPa Temperature Hardness (x of5) Room T. 19.51 200° C. 16.45 400° C. 15.42 600° C. 14.02 800° C. 12.171000° C.  10.17

At room temperature, this Example No. 5 material has a Rockwell Ahardness ranging from about 94.2 to about 94.8, a Vickers hardnessranging from about 17.0 to about 19.5 GPa, a K_(IC)−E+C fracturetoughness of about 5.0 to about 6.5 MPam^(1/2), and a density of about3.65 to 3.69 g/cc.

Thus, it is apparent that the present ceramic material is an improvedwhisker-reinforced ceramic material, and especially a whisker-reinforcedceramic material useful as a cutting tool, that contains aluminumoxynitride. Further, it is apparent that the present ceramic is animproved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride wherein the whisker exhibit satisfactorypull-out. In addition, it is apparent that the present ceramic materialis an improved whisker-reinforced ceramic material, and especially awhisker-reinforced ceramic material useful as a cutting tool, thatcontains aluminum oxynitride wherein the hot-pressing of the powdermixture occurs at a temperature low enough so as to not damage thesilicon carbide whiskers. Finally, it is apparent that the presentceramic is an improved whisker-reinforced ceramic material, andespecially a whisker-reinforced ceramic material useful as a cuttingtool, that contains aluminum oxynitride wherein there is control overthe amount of aluminum oxynitride in the ceramic.

The patents and other documents identified herein are herebyincorporated by reference herein. Other embodiments of the inventionwill be apparent to those skilled in the art from a consideration of thespecification or a practice of the invention disclosed herein. It isintended that the specification and examples are illustrative only andare not intended to be limiting on the scope of the invention. The truescope and spirit of the invention is indicated by the following claims.

1. A process of making aluminum oxynitride powder comprising the stepsof: forming a powder mixture by mixing alumina powder and aluminumnitride powder according to the following formula: ((4-x)/3) alumina andx aluminum nitride wherein x is in mole percent and ranges between about0.31 and about 0.61; adding between about 0.1 mole percent and about 1.0mole percent of pure aluminum powder to the powder mixture; and reactingthe powder mixture containing aluminum at a temperature between about1600° C. and about 1900° C. for a duration between about 2 hours andabout 24 hours in a flowing nitrogen atmosphere so as to form aluminumoxynitride.
 2. The process of claim 1 wherein the aluminum oxynitridehas the formula: Al_((8+x)/3)O_(4−x)N_(x).
 3. The process of claim 1wherein the pure aluminum powder added to the powder mixture rangesbetween about 0.1 to about 0.2 mole percent.
 4. The process of claim 1wherein the aluminum oxynitride contains less than or equal to about 0.1weight percent aluminum nitride.
 5. The process of claim 1 wherein xequals about 0.35.
 6. The process of claim 5 wherein the pure aluminumpowder added to the powder mixture ranges between about 0.1 to about 0.2mole percent.